1. Field of the Invention
The invention relates to a heat assist magnetic write head used in heat assist magnetic recording in which near-field light is irradiated to lower a coercivity of a magnetic recording medium so as to perform writing of information, and to a head gimbals assembly, to a head arm assembly, and to a magnetic disk device provided with the same.
2. Description of the Related Art
A magnetic disk device has been heretofore used as a device which performs writing and reading of magnetic information (hereinafter simply referred to as information). The magnetic disk device is provided, inside of a housing, for example, with a magnetic disk into which the information is stored, and a magnetic read write head which performs writing of the information on the magnetic disk and which performs reading of the information written in the magnetic disk. The magnetic disk is supported on a rotary shaft of a spindle motor secured to the housing, and is rotated therearound. On the other hand, the magnetic read write head is formed on one side face of a magnetic head slider provided on one end of a suspension, and is configured by including a magnetic write element and a magnetic read element that have an air-bearing surface (ABS: Air Bearing Surface) opposed to the magnetic disk. For the magnetic read element, an MR element which exhibits a magnetoresistive (MR: Magnetoresistive) effect has been generally used, in particular. The other end of the suspension is attached to a tip of an arm rotatably supported on a fixed shaft which stands in the housing.
The magnetic read write head is not present on the magnetic disk and is in a state (an unload state) where it is retracted to the outside, when the magnetic disk device is in a stationary state, i.e., when the magnetic disk does not rotate and remains at rest. Herein, when the magnetic disk device is in a drive state and the magnetic disk starts to rotate, the magnetic read write head is in a state (a loaded state) where it is moved together with the suspension to a predetermined position on the magnetic disk. When the magnetic disk reaches the predetermined number of rotation, the magnetic head slider becomes stable in a state in which it flies slightly above a surface of the magnetic disk, thus making it possible to write and read the information accurately.
In recent years, with a progress in higher recording density (higher capacity) of the magnetic disk, an improvement in performance of the magnetic read write head as well as the magnetic disk has been demanded accordingly. The magnetic disk is a discrete medium in which magnetic fine particles are aggregated, and each of the magnetic fine particles has a single-domain structure. In this magnetic disk, a single recording bit is structured by a plurality of magnetic fine particles. In order to improve the recording density, it is necessary to reduce asperities at boundaries between the adjoining recording bits. Hence, it is necessary to make the magnetic fine particles smaller. However, making the magnetic fine particles smaller causes an issue that a thermal stability of magnetization of the magnetic fine particles decreases with decreasing volume of the magnetic fine particles. To solve this issue, it is effective to increase anisotropic energy of the magnetic fine particles. However, increasing the anisotropic energy of the magnetic fine particles leads to an increase in coercivity of the magnetic disk, and here rises an issue that this makes it difficult for an existing magnetic head to write the information.
To solve the foregoing issues, there has been proposed a method so-called heat assist magnetic recording. This method uses a magnetic recording medium having a high coercivity. When writing the information, a magnetic field as well as heat are applied simultaneously to a region of the magnetic recording medium where the information is to be written, to increase a temperature of that region to decrease the coercivity so as to perform the writing of the information. Hereinafter, a magnetic head used in the heat assist magnetic recording will be referred to as a heat assist magnetic write head.
In the heat assist magnetic recording, a method which utilizes near-field light is typically used as a way of applying the heat to the magnetic recording medium. As a method of generating the near-field light, a method is generally known, which uses a near-field optical probe or a so-called plasmon generator, which is a piece of metal that generates the near-field light from plasmons excited by irradiation of light. However, the plasmon generator which generates the near-field light by the direct irradiation of light is known to exhibit very low efficiency of transformation of the irradiated light into the near-field light. The energy of the light irradiated to the plasmon generator is mostly reflected off a surface of the plasmon generator, or is transformed into thermal energy and absorbed by the plasmon generator. The plasmon generator is small in volume since a size of the plasmon generator is set to be equal to or smaller a wavelength of the light. Thus, in the plasmon generator, a rise in temperature due to the absorption of the thermal energy described above becomes significantly large.
Incidentally, for the heat assist magnetic recording, it is desired that a position of generation of a write magnetic field and a position of generation of the near-field light be located as close as possible in a medium facing surface. For example, U.S. Patent Application Publication No. 2007/139818 specification discloses a magnetic head in which a near-field light generating part that generates near-field light when irradiated with laser light and an end of a main magnetic-pole layer are arranged to be laid over each other directly or with a dielectric layer therebetween in a medium facing surface. Also, U.S. Patent Application Publication No. 2009/168220 specification discloses a magnetic head in which at least a part of a main magnetic pole is arranged between a first and a second near-field light generating part each of which generates near-field light when irradiated by laser light. However, when the main magnetic pole for generating the write magnetic field and the plasmon generator for generating the near-field light are arranged closely, the main magnetic pole is heated due to the rise in the temperature of the plasmon generator. As a result, the main magnetic pole is likely to corrode by moisture in the atmosphere depending on an ambient humidity condition.
Therefore, it is desirable to suppress the corrosion of the main magnetic pole due to the temperature rise to ensure long-term reliability, while maintaining performance in writing.